| In this paper,graphene oxide-based calcium alginate beads and its magnetic beads were prepared by using the advantages of graphene oxide and sodium alginate to adsorb heavy metal cations.The beads’ adsorption characteristics of heavy metal copper ions and cadmium ions in aqueous solutions were studied,and the amount of the beads,the adsorption time,pH values and other conditions were optimized.Meanwhile,a graphite furnace atomic absorption spectrometry for the detection of cadmium ions in oyster homogenates was established.Magnetic graphene oxide-based calcium alginate beads were applied to the adsorption of cadmium ions in real food samples of oyster homogenate.The digestion conditions of oyster homogenate,the extraction conditions of citric acid and the adsorption conditions of the beads were optimized.The main contents and results are as follows:1.The preparation and characterization of the two kinds of beads.Graphene oxide-based calcium alginate beads and its magnetic beads were prepared by using several raw materials such as sodium alginate,calcium chloride,ferric chloride,ferrous chloride and graphene oxide which was prepared by Hummers’ method.Then they were characterized by FT-IR,SEM and XRD.The SEM result shows that the two kinds of beads are spherical in shape and their diameters are approximately 1875um and 933um,respectively.Their surfaces are wrinkled and their interior structure are faveolate.These could greatly increase the specific surface area of adsorbing heavy metal ions,so that they can be fully combined with the active spot.The X-ray diffraction results show that the molecular chains of sodium alginate intercalate into graphene oxide layer,which forms the interlayer structure,resulting in the further increase of the gap between the layers of graphene oxide.2.The study of the adsorption of cadmium and copper by the two kinds of beads in aqueous solution.The adsorption tests were respectively carried out on the aqueous solution containing copper ions and the aqueous solution containing cadmium ions by using the two kinds of beads as adsorbents.The adsorption characteristics of heavy metal ions were determined by flame atomic absorption spectrometry.The results show that the best adsorption conditions for copper ion aqueous solution are as follows:the amounts of adsorbent are 0.06 g and the values of pH are 6,the time are 4h and 3h,respectively.The optimal adsorption conditions for cadmium ion aqueous solution are as follows;the amounts of adsorbent are 0.08 g and the values of pH are 7 and the times are 4 h.What’s more,the experimental data were fitted by using first-order kinetic model,second-order kinetic model and intra-particle diffusion model.It could be found that the adsorption of copper ions by the two kinds of beads is more in line with the second-order kinetic model.These two models’ R2 are 0.9978 and 0.9983 respectively,and the adsorption rates of the two beads are 0.0040 mg/(g.min)and 0.0038 mg/(g.min),respectively.The calculated equilibrium adsorption capacities of the two beads are 48.31 mg/g and 49.50 mg/g,respectively,which are in agreement with the experimental equilibrium adsorption capacities of 47.8 mg/g and 48.8 mg/g.It is further verified that the adsorption of copper ions is more in line with the second-order kinetic model.The adsorption of cadmium ions is more in line with the second-order kinetic model,too.R2 are 0.9996 and 0.9995,and the adsorption rates are 0.0040 mg/(g.min)and 0.0038 mg/(g.min),respectively.The calculated equilibrium adsorption capacities are 48.31 mg/g and 49.50 mg/g,respectively,which are in agreement with the experimental equilibrium adsorption capacities of 47.8 mg/g and 48.8 mg/g.The isothermal adsorption of copper and cadmium ions by the two kinds of beads is fitted by Lanmuir model and Frundlich model.It is found that the Lanmuir model can better describe the adsorption of copper ions and cadmium ions by they.Therefore,the adsorption of copper ions and cadmium ions by the beads is performed in the form of monolayer adsorption.3.Determination of cadmium in oyster homogenate by graphite furnace atomic absorption spectrometry.The oyster homogenate was digested respectively by wet digestion and microwave digestion in order to select the best digestion scheme.The cadmium content in the oyster homogenate by wet digestion is 0.3166 mg/kg,and the recovery rate is 80.50%.The cadmium content in the oyster oyster by microwave digestion is 0.3430 mg/kg,and the recovery rate is 94.17%.The microwave digestion time is short,the operation of it is convenient,and the recovery result is excellent,so microwave digestion is used to digest the oyster homogenate.4.Adsorption of cadmium ions in oyster homogenate by magnetic graphene oxide-based calcium alginate beads.After using orthogonal method,we have obtained the best way to extract oyster homogenate by citric acid,which is as follows:Citric acid concentration is 0.08mol/L,ratio of material to liquid is 1:5,the extraction time is 6h.At this time,the extraction rate was 89.03%.In order to optimize the optimal conditions for adsorption of cadmium in the extract of oyster homogenate by magnetic beads,single factor experiments were carried out by treating the solution pH,the amount of magnetic beads added,and the time as important factors.The results showed that when the pH was 4,the amount of magnetic beads was 0.06g and the time was 5h,the adsorption effect was the best,and the adsorption rate was 93.32%at this time. |
